Method for curing resin

ABSTRACT

In a method for curing a resin by utilizing an intermolecular crosslinking reaction, the improvement wherein the crosslinking reaction is a a ring opening addition reaction between a lactone structure and an active hydrogen-containing functional group.

This applicatin is a Continuation application of Ser. No. 08/297,517,filed Aug. 29, 1994 which in turn is a Continuation application of Ser.No. 07/645,253, filed Jan. 24, 1991, both applications being abandoned.

This invention relates to a novel method for curing a resin.

There has been hitherto well known a method for three-dimensionallycrosslinking and curing a synthetic resin by using a curing agent(crosslinking agent) such as a melamine resin or a polyisocyanatecompound. However, when using the melamine resin, by-products such asalcohols, aldehydes, water, etc. occur during a curing reaction,deteriorating physical properties of a cured product. Meanwhile, whenusing the polyisocyanate compound, a system is a two-package systemwhich is intricate to treat.

The present inventors have made extensive studies to eliminate the aboveconventional defects in curing the synthetic resin and develop a novelcuring method in which a system is a one-package system and occurrenceof by-products is little observed in the curing reaction. As a result,they have this time found that the above object can be achieved by acuring method chiefly utilizing a ring opening or addition reaction of alactone structure, and completed this invention.

Thus, according to this invention, there is provided a method for curinga resin by utilizing an intermolecular or intramolecular crosslinkingreaction of a resin, characterized in that the crosslinking reaction isa ring opening-polymerization reaction between lactone structures and/ora ring opening addition reaction between a lactone structure and anactive hydrogen-containing functional group.

The resin is generally crosslinked and cured by, for example, chemicallybonding molecules of a resin having a straight-chain structure(including also a chain structure with a branched chain) inthree-dimensional network such that the molecules of said resin arebridged intermolecularly and/or intramolecularly.

This invention is characterized in that the resin is crosslinked andcured chiefly utilizing a ring opening reaction of a lactone structurecontained in a straight-chain resin. The lactone structure is preferablya 4- to 9-membered cyclic functional group having an ester linkage in aring. In one aspect of this invention, the resin is presumablycrosslinked and cured such that the lactone ring is opened at the esterlinkage site either by heating or with a catalyst, and then attacks theother lactone structure to form a polyester structure (ring openingpolymerization), as shown in the following reaction scheme A. ##STR1##wherein R denotes a saturated aliphatic hydro-carbon group havingpreferably 2 to 7 carbon atoms, ##STR2## denotes a resin body and R'denotes an alkyl group such as an ethyl group.

In another aspect of this invention, the lactone structure can besubjected to a ring opening addition reaction with activehydroxyl-containing functional groups such as a hydroxyl group, acarboxyl group and an amine group, thereby crosslinking and curing theresin.

The crosslinking and curing reaction between the lactone structure andthe active hydrogen-containing functional group is thought to typicallyproceed as shown in the following reaction scheme B. ##STR3## wherein##STR4## is as defined above.

As the crosslinking and curing reaction usually little proceeds at roomtemperature, there are advantages that a resin which can be curedaccording to this invention is excellent in storage stability and usableas a one-package type. Moreover, compared with an ordinary method forcuring a resin with a curing agent such as an amino resin, etc., themethod of this invention little or never allows formation of by-productsin the crosslinking and curing reaction. In consequence, when the methodof this invention is applied to paints, a coating surface havingexcellent smoothness can be formed and an internal stress of a coatingfilm is low so that a coating surface excellent in adhesion to a surfacebeing coated can be provided.

The lactone structure can be formed by the following methods which areknown per se. However, they are not critical in this invention.

(1) Formation by an oxidation reaction and a reduction reaction

(a) Formation by peroxidation of a cyclic ketone

A cyclic ketone enlarges the ring and forms a lactone by a peracid.

(b) Formation by oxidation of a cyclic ether

A cyclic ether is oxidized with chromic acid, t-butyl chromate orruthenium oxide to form a lactone.

(c) Formation by reduction of an acid anhydride

When an acid anhydride is reduced with metallic sodium-alcohol, lithiumaluminum hydride or lithium aluminum tri-t-butoxy hydride, a lactonestructure is formed. It is also formed usingchlorotris-(triphenylphosphine) rhodium.

(2) Formation by ring closure of a carboxylic acid or its derivatives

(a) Formation from a hydroxycarboxylic acid or its esters

When a hydroxycarboxylic acid is treated with an acid, dehydration takesplace to form a lactone. For example, a gamma-hydroxycarboxylic acid anda delta-hydroxycarboxylic acid provide a gamma-lactone and adelta-lactone respectively. Examples of the acid are mineral acids suchas sulfuric acid and hydrochloric acid, and organic acids such asp-toluenesulfonic acid. The lactone can be formed using an acidanhydride (e.g. acetic anhydride and trifluoroacetic anhydride) orphosgene.

(b) Formation from an unsaturated carboxylic acid or its esters

A beta,gamma-unsaturated carboxylic acid is easily ring-closed in thepresence of an acid to form a gamma-lactone. Examples of the acid aresulfuric acid and trifluoroacetic acid. 4-Pentenoic acid forms agamma-lactone and 5-methyl-4-hexenoic acid forms a gamma-lactone. Whenan olefinic carboxylic acid is reacted with a peracid, a hydroxylactoneis formed. Moreover, an ester having a cyclopropyl group can belactonized with an acid.

(c) Formation from an olefinic diazo ester

A carbene formed by decomposition of a diazo ester having a double bondis added to a double bond in a molecule to form cyclopropyl lactone. Adiazo malonic acid ester also forms a lactone. A compound having acyclopropylcarbonyl group can be converted into a gamma-lactone with acyclopropane ring cleaved.

(3) Formation by carbonylation and introduction of a carboxylic acidresidue

(a) Formation by carbonylation of acetylene carbinol

When an alcohol having terminal acetylene is carbonylated, a lactone isformed. For example, when beta-hydroxyacetylene is carbonylated withcarbon monoxide, alpha-methylene lactone results, and butenolyd isformed from ethenyl carbinol. Further, when vinyl alcohol iscarbonylated, a lactone is obtained.

(b) Formation by a reaction between a ketone and a ketene

An aldehyde or a ketone is condensed with a ketene in the presence of aLewis acid as a catalyst to form a beta-lactone. Dimethyl ketene iscondensed with cyclopropane to form spiro-beta-lactone. Dichloroketeneis concensed with an aldehyde to form alpha,alpha-dichloro-beta-lactone.An unsaturated delta-lactone is formed by a reaction of analpha,beta-unsaturated aldehyde and/or a ketone with a ketene.

(c) Formation by introduction of a carboxylic acid residue into anepoxide

Active methylene compounds such as a malonic acid ester, ethylcyanoacetate and ethyl acetoacetate form corresponding gamma-lactonederivatives respectively. Oxirane is condensed with a ketene to form agamma-lactone.

As a method to bond the thus formed lactone structure to a resinmolecule, it is possible to introduce a substituent in the lactonestructure and chemically bond the lactone structure to a resin substrateutilizing the substituent. The substituent is introduced into thelactone structure by e.g. carboxylation or hydroxymethylation of analpha-position of the lactone ring. A hydroxyl group can be added bysubjecting a beta-position of the lactone ring to a Michaelcondensation. An isocyanate group can also be introduced by adding apolyisocyanate compound to the hydroxyl group.

The substituent (e.g. a hydroxyl group, a carboxyl group and anisocyanate group) introduced into the lactone structure as above isreacted with a functional group introduced in the resin substrate,thereby making it possible to introduce the lactone into the resinsubstrate. Time functional group that can be introduced into the resinsubstrate may be any group that is mutually reacted with the substituentof the lactone structure. Examples of such group are a hydroxyl group, acarboxyl group, an epoxy group and an isocyanate group. The resinsubstrate into which these functional groups are introduced is notlimited in particular, and can optionally be selected depending on theuse purpose of the resin. Examples thereof are an acrylic resin, a vinylresin, a polyester (alkyd) resin, a polyamide resin, a polyurethaneresin, an epoxy resin and a fluorine resin. It is advisable that theresin substrate has a number average molecular weight of usually 200 to100,000, preferably 200 to 50,000 and more preferably 200 to 20,000. Theabove functional group can be introduced into such resin substrate in amanner known per se.

A preferable combination of the functional group of the resin substratefor introducing the lactone structure into the resin substrate and thesubstituent of the lactone structure is listed below.

    ______________________________________                                        Functional group of                                                                           Substituent of a                                              a resin substrate                                                                             lactone structure                                             ______________________________________                                        Hydroxyl group  Carboxyl group, epoxy group,                                                  isocyanate group                                              Carboxyl group  Hydroxyl group, amino group,                                                  epoxy group                                                   Epoxy group     Carboxyl group, hydroxyl                                                      group, thiol group, amino                                                     group, hydroxyl group                                         Isocyanate group                                                                              Hydroxyl group, amino group                                   ______________________________________                                    

Another method to introduce the lactone structure into the resinsubstrate is that a polymerizable unsaturated monomer containing alactone structure is singly polymerized or copolymerized with anotherpolymerizable monomer. Examples of the polymerizable unsaturated monomercontaining the lactone structure are monomers represented by formulas##STR5## wherein R₁ denotes H or CH₃ and R₂ denotes a C₁₋₈ hydrocarbongroup.

The other monomer copolymerizable with these monomers is preferably thepolymerizable unsaturated monomer (the vinyl monomer or the acrylicmonomer) used in forming the vinyl resin or the acrylic resin.

Further, when maleic anhydride is copolymerized with allyl alcohol, ringclosure is conducted in polymerization to obtain a lactonestructure-containing vinyl polymer as shown in the following reactionscheme C. ##STR6##

The number of the lactone structure being introduced can be at least 2,preferably 3 to 30, more preferably 5 to 15 per molecule.

In the method of this invention, a resin having a lactone structure andan active hydrogen-containing group per molecule is also available. Whenusing such resin, the lactone structures or the lactone structure andthe active hydrogen-containing functional group cause the intermolecularor intramolecular ring opening bonding reaction to conduct crosslinkingand curing.

Such resin can be formed by reacting part of the functional group of theresin substrate having introduced therein the active hydrogen-containingfunctional group with the substituent of the lactone structure. Saidresin can contain at least 1, preferably 3 to 30, more preferably 5 to15 lactone structures and at least 1, preferably 3 to 10, morepreferably 5 to 15 active hydrogen-containing functional groups.

Further, in the method of this invention, a mixture of the aforesaidlactone structure-containing resin and the resin having the activehydrogen-containing functional group is also available.

As the active hydrogen-containing functional group, a hydroxyl group, acarboxyl group and an amino group are most preferable to expedite thecrosslinking reaction with the lactone structure. A hydrosilyl group anda thiol group are also available.

The resin having the active hydrogen-containing functional group can beproduced, for example, by polymerizing or adding the compound having theactive hydrogen-containing functional group in or after forming theresin substrate as above.

The resin having the active hydrogen-containing functional group has anumber average molecular weight of usually 500 to 100,000, preferably1,000 to 50,000, more preferably 2,000 to 30,000. The number of theactive hydrogen-containing functional group is at least 2, preferably 3to 30, more preferably 5 to 15 per molecule.

The method of this invention crosslinks and cures the resin basedchiefly on the ring opening reaction of the lactone structure. To beconcrete, the ring opening polymerization reaction between the lactonestructures (see Reaction Scheme A) and the ring opening additionreaction of the lactone structure and the active hydrogen-containingfunctional group (see Reaction Scheme B) are taken. This inventioncrosslinks and cures the resin by the reaction based on one or both ofthese reactions.

Accordingly, it is advisable to perform the method of this inventionusing the following resins (A) to (C) either singly or in combination oftwo or more.

(A) A resin containing per molecule at least 2, preferably 3 to 30, morepreferably 5 to 15 (or per kg of the resin, 0.1 to 15 mols, preferably0.3 to 10 mols, more preferably 1.0 to 5 mols of) lactone structures.

(B) A mixture of the resin (A) and a resin containing per molecule, atleast 2, preferably 3 to 30, more preferably 5 to 15 (or per kg of theresin, 0.1 to 15 mols, preferably 0.3 to 10 mols, more preferably 1.0 to5 mols of) active hydrogen-containing functional groups. The amount ofthe resin (A) is usually 5 to 95% by weight, preferably 20 to 50% byweight based on the total weight of both the resins (A) and (B), and theamount of the resin B, is usually 95 to 5% by weight, preferably 50' to20% by weight on the same basis.

(C) A resin containing a lactone structure and an activehydrogen-containing functional group in a molecule. The lactonestructure/active hydrogen-containing functional group molar ratio isusually 5/1 to 1/5, preferably 3/1 to 1/3.

In the aspect of curability, the resin (C) is best, the resin (A) isbetter and the resin (B) is good.

In the method of this invention, the conditions for crosslinking andcuring the resin selected from the resins (A) to (C) vary with thelactone structure. The heating (baking) temperature is usually at least80° C., especially preferably 140° to 200° C. When heating is conductedat the above temperature usually for 10 to 30 minutes, the resin iscrosslinked and cured.

In order to decrease the crosslinking and curing temperature or shortenthe heating temperature, said resin may be blended with the followingcatalyst in an amount of 0.01 to 10 parts by weight per 100 parts byweight of the resin.

1. Catalyst for anionic polymerization:

For example, Li, Na, K, Na-naphthalene, Li₂ -benzophenone, K₂-benzophenone, LiR, NaR, LiH, NaH, K₂ CO₃, KOH, NaOR, LiOR, acetates ofLi, Na and K, and tertiary amines such as pyridine, picolin andquinoline.

2. Catalyst for coordination anionic polymerization:

For example, AlR₃, ZnR₂, MgR₂, RMgX, R₂ AlX, RAlX₂, R₂ Al (OR'), AlEt₃--H₂ O, Zn(C₂ H₅)₂ --H₂ O, Cd(C₂ H₅)₂ -H₂ O, Al(OR)₃, Mg(OR)₂, Ti(OR)₄and titanium phosphate.

3. Catalyst for cationic polymerization:

AlCl₃, BF₃.(C₂ H₅)₂ O, other metal halides, CF₃ CO₂ H, acetylperchlorate, toluenesulfonic acid and phosphoric acid.

In the above description, R and R' each denote a hydrocarbon grouphaving 1 to 10 carbon atoms and X denotes a halogen atom.

In the method of this invention, the resins (A) to (C) can be blendedwith a coloring pigment, a metallic pigment and an extender pigment. Itis advisable that the resin is used by being dissolved or dispersed inan organic solvent and/or water.

Moreover, it is also possible, if required, to asdd to said resin alow-molecular polyol (a number average molecular weight less than 500)such as glycol or triol and a lactone compound (a number averagemolecular weight less than 500) such as valerolactone or caprolactone.

The method of this invention can advantageously be utilized in the fieldof paints, ink, adhesives, tackifiers and molded articles.

PREPARATION EXAMPLE 1

A vinyl monomer (212 g: 1 mol) represented by formula, ##STR7## 400 g ofmethyl methacrylate, 130 g of 2-hydroxyethyl methacrylate and 256 g ofethyl acrylate were copolymerized to form a vinyl resin (1) having anumber average molecular weight of 15,000.

This resin contains 1 mol/kg of a caprolactone structure and 1 mol/kg ofa primary hydroxyl group.

PREPARATION EXAMPLE 2

A compound (260 g: 2 mols) of a structure represented by formula##STR8## was reacted with 730 g of a polyurethane resin with terminalNCO of a hexamethylenediisocyanate type to form a polyurethane resin (2)containing a terminal valerolactone structure and having a numberaverage molecular weight of 5,000.

This resin contains 2 mols/kg of the valerolactone structure.

PREPARATION EXAMPLE 3

One thousand grams of a bisphenol A-type diepoxy resin having a numberaverage molecular weight 1,000 was reacted with 2 mols of ketene in thepresence of a catalytic amount of trifluoroboron etherate to introduce abutyrolactone structure in the end. ##STR9##

This resin (3) contains 1.85 mols/kg of the butyrolactone structure and1.85 mol/kg of a secondary hydroxyl group.

PREPARATION EXAMPLE 4

A compound (432 g: 3 mols) of a structure represented by formula##STR10## was condensed with 300 g of a polyester resin with a terminalcarboxyl group having a number average molecular weight of 3,000 to forma polyester resin (4) containing a caprolactone structure and having amolecular weight of 3,500.

This resin contains 0.57 mol/kg of the caprolactone structure and 1.0mol/kg of the carboxyl group.

PREPARATION EXAMPLE 5

Hydrogenated bisphenol A was oxidized into a diketone which was thenreacted with peracetic acid to obtain a resin (5) of a structurerepresented by the formula. ##STR11##

This resin contains 7.5 mols/kg of caprolactone and has a number averagemolecular weight of 268.

PREPARATION EXAMPLE 6

2-Hydroxyethyl acrylate (17.2 parts), 30 parts of styrene and 52.8 partsof n-butyl acrylate were added dropwise together with 4 parts ofazobisisobutylonitrile to 100 parts of xylol (solvent) heated at 110° C.over about 3 hours. Thereafter, the mixture was aged at the sametemperature for 3 hours to obtain a hydroxyl group-containing copolymer(6) having a number average molecular weight of about 18,000.

PREPARATION EXAMPLE 7

Dimer acid and ethylenediamine were subjected to dehydrocondensationreaction at 200° C. at a dimer acid/ethylenediamine molar ratio of 1/1.2to obtain an amino group-terminated polyamide resin (7) having amolecular weight of about 1,000.

EXAMPLES

(a) The resin (1) alone was baked at 170° C. for 60 minutes.

(b) The resin (2) and the hydroxyl group-containing copolymer (6) weremixed at a weight ratio of 1:1, and 0.1% of tetrabutyl titanate wasadded thereto. The mixture was baked at 120° C. for 30 minutes.

(c) AlCl₃ (3%) was added to the resin (3) alone, and the mixture wasbaked at 200° C. for 30 minutes.

(d) The resin (4) was mixed with 30% of epsilon-caprolactone, and 1% oftris(acetylacetonato)aluminum was added thereto. The mixture was bakedat 140° C. for 30 minutes.

(e) The resin (5) and the amino group-terminated polyamide resin (7)(HH₂ 2 mols/kg) were mixed at a weight ratio of 1:1, and the mixture wasbaked at 200° C. for 30 minutes.

The characteristics of the crosslinked cured resins obtained in (a) to(e) are tabulated below.

    ______________________________________                                               (a)    (b)      (c)      (d)   (e)                                     ______________________________________                                        Wiped 20 No       No       Gloss  No    No                                    times with                                                                             change   change   slightly                                                                             change                                                                              change                                xylol                      loses                                              Tukon    18       10       5.5    8     11                                    hardness                                                                      ______________________________________                                    

What we claim is:
 1. In a method for curing a resin by utilizing anintermolecular cross-linking reaction, the improvement wherein thecross-linking reaction is initiated by the ring opening of a lactonering and addition reaction with an active hydrogen-containing functionalgroup involvinga mixture of (A-1) a resin containing at least two 4- to9-membered lactone rings per molecule and (A-2) a second resincontaining at least two active hydrogen-containing functional groupsselected from the group consisting of a hydroxyl group, a carboxyl groupand an amino group and having a number average molecular weight of 1,000to 50,000; said lactone rings each being bound to a main chain of theresin as pendant and/or terminal groups.
 2. The method of claim 1wherein the resin (A-1) contains 5 to 15 lactone rings per molecule. 3.The method of claim 1 wherein curing is conducted at a temperature of140° to 200° C.
 4. The method of claim 1 wherein the resin (A-2)contains 5 to 15 active hydrogen-containing functional groups.
 5. Themethod of claim 1 wherein there are 3 to 30 lactone rings per moleculepresent in resin (A-1) and 3 to 30 active hydrogen-containing functionalgroups per molecule in resin (A-2).
 6. The method of claim 1 wherein themixture is a mixture of a polyurethane resin containing lactone ringsand an acrylic resin containing hydroxyl groups.
 7. The method of claim1 wherein the (A-1) and (A-2) resins each are selected from the groupconsisting of acrylic resins, vinyl resins, polyester (alkyd) resins,polyamide resins, polyurethane resins, epoxy resins and fluorine resins.